The disclosures of Japanese Patent Applications Nos. 2000-312829 filed on Oct. 13, 2000 and 2000-346328 filed on Nov. 14, 2000, each including the specification, drawings and abstract, are incorporated herein by reference in their entirety.
1. Field of Invention
The present invention relates to a method of manufacturing an endless metallic belt, an apparatus for manufacturing the endless metallic belt, and the endless metallic belt manufactured by the method. The present invention is applicable to the manufacture of an endless metallic belt of a CVT (continuously variable transmission) such that the belt has a high degree of accuracy in its circumferential length.
2. Description of Related Art
An endless metallic belt is mounted on two rollers for traveling. When traveling on a roller, the belt is subjected to a tensile bending stress at its outer peripheral surface. When leaving the roller toward the next roller, the belt is straightened and is relieved of the tensile stress at the outer peripheral surface resulting from bending. During traveling, the outer peripheral surface of the belt is thus repeatedly subjected to the tensile stress by bending. It is therefore desired to improve fatigue strength of the belt against such repeated tensile stresses.
Japanese Patent Laid-Open Publication Nos. 61-42402 and 63-96258 propose an endless metallic belt with improved fatigue strength at its outer peripheral surface. More specifically, only the outer peripheral surface of the endless metallic belt is subjected to shot peening so as to produce a compressive residual stress at the outer peripheral surface, thereby improving the fatigue strength.
In an endless metallic belt formed from a thin metallic sheet, a plastic-deformation layer formed adjacent to each of the outer and inner circumferential surfaces has a thickness (e.g., about 20-25 (m) which is not negligible in view of a relatively small entire thickness (e.g., about 0.2 mm) of the belt. Accordingly, the endless metallic belt suffers from undesirable changes in its overall configuration, for instance, an increase (e.g., about 2 mm) of its circumferential length (e.g., about 720 mm), and a change of its crowing value R. The crowing value R is represented by a radius of curvature of the belt in cross section in a plane perpendicular to the circumferential direction, as indicated in cross sectional view of FIG. 1B, which is taken along line 1Bxe2x80x941B in the perspective view of FIG. 1A.
The endless metallic belt is usually required to have high geometrical and dimensional accuracies with respect to the circumferential length and crowing value R. However, the shot peening treatment, if applied to the endless metallic belt, causes a variation in the dimensional accuracy, which is added to a variation in the dimensional accuracy of the belt prior to the shot peening treatment, giving rise to a functional problem of the belt as the end product.
The accuracy of the circumferential length of the endless metallic belt is extremely important, particularly where the belt as the end product is a multi-layered belt consisting of a multiplicity of endless metallic layers (e.g., nine layers). Where the tolerance of a gap or clearance between the adjacent layers is 10 xcexcm, for example, the tolerance of a variation of the circumferential length of the belt is about 60 xcexcm, which is 2xcfx80 times the tolerance of the gap.
In the shot peening treatment, the shot peening intensity (defined by ejection velocity and density of shot peening particles) is instable in the initial and terminal periods of the shot peening operation. A variation or fluctuation in the shot peening intensity in the shot peening cycle causes local deterioration of the geometrical and dimensional accuracies of the belt such as a local variation of the circumferential length and a local variation of the crowing value R (radius of curvature in cross section perpendicular to the circumferential direction), since the endless metallic belt has a small thickness and is easily deformable, and since the shot peening operation is performed while the belt is rotating.
The local deterioration of the geometrical and dimensional accuracies of the endless metallic belt is further caused by a variation in the rotating speed of the belt during the shot peening treatment. Where the endless metallic belt during the shot peening treatment slips on rollers used for the shot peening treatment, the geometrical and dimensional accuracies of the belt have particularly large local variations.
Thus, an apparatus for manufacturing an endless metallic belt as disclosed in the above-identified publications suffers from relatively low reliability in terms of the geometrical and dimensional accuracies of the belt.
In view of the drawback indicated above, a multiplicity of endless metallic layers are prepared for manufacturing a multi-layered endless metallic belt, by assembling selected ones of those endless metallic layers, such that the circumferential lengths of the selected layers have a difference within a predetermined range of tolerance. However, this method requires a large volume of stock of the endless metallic layers, and suffers from extremely low manufacturing efficiency.
It is therefore an object of this invention to provide a method of manufacturing an endless metallic belt, which assures improved accuracy of the circumferential length of the belt while having a shot peening treatment applied thereto, which is conventionally a source of deterioration of the dimensional accuracy of the belt. Other objects of the invention are to provide an apparatus suitable for practicing the method, and the improved endless metallic belt manufactured by the method.
According to a first aspect of the present invention, there is provided a method of manufacturing an endless belt, comprising applying a shot peening treatment to the endless metallic belt, wherein the shot peening treatment includes a condition of the shot peening treatment is adjust to adjust a circumferential length of the endless metallic belt.
The method according to the first aspect of this invention permits improved efficiency in manufacturing of the endless metallic belt with improved accuracy of its circumferential length, owing to the adjustment of the circumferential length by adjusting the condition of the shot peening treatment (for example, adjustment of the shot peening time).
Since the present method permits the adjustment of the circumferential length of each belt by adjusting the condition of the shot peening treatment, the endless metallic belt manufactured by this method can be suitably used as each element of a multilayered endless metallic belt including multiple elements in the form of multiple endless metallic layers. Therefore, this method permits improved efficiency in manufacturing of such a multi-layered endless metallic belt, without maintaining a large volume of stock of endless metallic layers as required in the prior art (which requires selection of a group of endless metallic layers whose circumferential lengths are almost equal to each other).
In accordance with the invention, the improved endless metallic belt can be manufactured by the method described above.
Further, the method described above can be practiced, for example, by an apparatus comprising: at least two rollers upon which the endless metallic belt rotates in tension; an ejection nozzle that ejects shot peening particles against the endless metallic belt during rotation of the endless metallic belt during a shot peening treatment; and an instrument that measures a variation of a circumferential length of the endless metallic belt during the shot peening treatment. Alternatively, the method can be practiced by an apparatus comprising: at least two rollers upon which the endless metallic belt rotates in tension; an ejection nozzle that ejects shot peening particles against the metallic belt during rotation of the endless metallic belt during a shot peening treatment; and a blocking mechanism that prevents the shot peening particles from striking the endless metallic belt.